This invention relates to a method and apparatus for illuminating a graphical display with a light source and a light guide including scattering elements to increase the light efficiency for an instrument gauge display.
An instrument cluster for a vehicle is traditionally located on a vehicle dashboard and includes several gauges or dials that indicate various vehicle operating conditions. For example, an instrument cluster may include a speedometer, a tachometer, an engine condition indicator, and other known types of gauges. These gauges are illuminated to facilitate reading of the information by the vehicle occupants.
Instrument clusters include a printed circuit board (PCB) with electronic components for controlling operation of the instrument clusters. Light sources are typically mounted to the PCB. A light box or light housing is used to contain the light produced by the light sources inside the instrument cluster and prevents unwanted light leakage. The light housing is also used to distribute the light from the light source over the graphical area to be illuminated.
The instrument cluster further includes display or dial on which the graphical image is formed or mounted. Typically, the dial is formed from a transparent material that has an upper surface partially covered by a layer black paint and a lower surface covered by a layer of white paint. The uncovered upper surface areas define the graphical images. During reduced light levels of operation, it is common to illuminate all of the area underneath the graphical images.
Improvements in the area of optics over the years has resulted in a significant increase in light output from light sources. This has significantly reduced the number of light sources needed to adequately illuminate a graphical display. However, this increased light output has also made it more difficult to evenly distribute luminance over the display without requiring some form of compensation.
Compensation usually involves the addition of coatings or layers of material applied to at least one of the gauge components to absorb light in certain areas. In one example, an additional layer of black dots is applied to the dial in the areas of bright illumination, i.e. the areas closest to the light source. This layer of dots is typically placed on top of the white paint layer, which is applied to the bottom surface of the dial. While this configuration provides for more even illumination, it is disadvantageous because light efficiency is decreased due to the light absorption.
Thus, there is a need for an instrument gauge display that provides a more even and bright graphical illumination in addition to overcoming the other above-mentioned deficiencies.